Steve Litt's Perls of Wisdom:
Simple Perl String and Numeric Manipulation Handling
(With Snippets)
Copyright (C) 2003 by Steve Litt
CONTENTS
Much of any computer language concerns manipulation and comparison of strings
and numbers. Perl has the usual complement of functions and operators for
both. Note that much Perl string manipulation is performed with regular expressions,
especially if performance is not an issue. Regular expressions are covered
in their own document. This document details non-regex
string handling.
Numeric Operators
Numeric manipulation is arithmetic. I won't give you Perl's order of precidence
-- I don't know it myself. I use parentheses liberally, ensuring the intended
calculation. Generally speaking, if you understand C or Java arithmetic,
you understand Perl's:
Operator
|
Functionality
|
Example
|
$var contains
|
=
|
Assignment
|
$var = 8;
|
8
|
+
|
Addition
|
$var = 8 + 3;
|
11
|
-
|
Subtraction
|
$var = 8 - 3;
|
5
|
*
|
Multiplication
|
$var = 8 * 3;
|
24
|
/
|
Fractional Division
(5/2 is 2.50, not 2)
|
$var = 8 / 3;
|
2.66666666666667
|
%
|
Modulus
|
$var = 8 % 3
|
2
|
|
Whole number division
|
$var = (8-(8%3))/3
|
2
|
Perl's numeric relational operators are similar to C's:
Operator
|
Functionality
|
Example
|
>
|
Numeric greater than
|
if($var > 8)
|
>=
|
Numeric greater than or equal
|
if($var >= 8) |
<
|
Numeric less than
|
if($var < 8) |
<=
|
Numeric less than or equal |
if($var <= 8) |
==
|
Numeric equality
|
if($var == 8) |
String Manipulation:
dot, length(), substr(), index() and rindex()
Use the dot operator to concatinate 2 strings:
$var = "George" . " " . "W." . " " . "Bush";
In the preceding, $var now contains "George W. Bush".
You often need the length of a string. Use the length() function
to get that.
The opposite of concatination is truncation. Personally, I do most truncation
with regular expressions, which are discussed in a different
document. However, you can also use the substr().substr()
is faster than regular expressions, so if you're truncating in a tight loop,
you might want to usesubstr(). Its syntax is as follows:
substr EXPR,OFFSET,LENGTH,REPLACEMENT
LENGTH and REPLACEMENT are optional. Personally, I seldom
use REPLACEMENT because it's clearer to replace text with a concatenation
after truncation. Here are some ways you can use substr() to truncate
from the right and from the left of a string. In the following examples,
imagine that:
$string = "Perl Programmer":
Task
|
Statement
|
Value of $var
|
Remove 3 characters from the front of the string
|
$var = substr($string, 3);
|
"l Programmer"
|
Remove all but the 3 final characters from the string
|
$var = substr($string", -3); |
"mer"
|
| Remove the 3 final characters from the string |
$var = substr($string, 0, - 3);
|
"Perl Program"
|
Remove all but the first 3 chaaracters from the string
|
$var = substr($string, 0, 3);
|
"Per"
|
To remove specific text, you can use the index()and rindex()
functions to find the offset of the start of a substring, and then plug that
number into the OFFSET or LENGTH arguments of substr(). Information
on length(), substr(), index() and rindex()are
contained in their respective man pages.
String Comparison Operators
Perl's string relational operators are distinct from its numeric relational
operators:
Operator
|
Functionality
|
Example
|
gt
|
String greater than
|
if($var gt "cccc")
|
ge
|
String greater than or equal
|
if($var ge "cccc") |
lt
|
String less than
|
if($var lt "cccc") |
le
|
String less than or equal |
if($var le "cccc") |
eq
|
String equality
|
if($var eq "cccc") |
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(C) 2003 by Steve Litt --Legal